The invention relates to an anti-friction bearing and especially an anti-friction bearing for supporting a shaft of a gear case for a portable handheld work apparatus.
Anti-friction bearings are known for supporting a rotating shaft which include a device for repelling a lubricant. The anti-friction bearing is essentially formed of an inner race and an outer race which surrounds the inner race at a radial spacing. Roller elements are provided radially between the inner race and the outer race. The shaft engages centrally through an eye of the inner race. An annular disc is mounted on the shaft to rotate therewith and is at an axial spacing to the anti-friction bearing. The annular disc functions to throw off lubricant, which reaches the roller bearing, with centrifugal force during the rotating operation of the shaft. If such an anti-friction bearing is built into a housing wall of a housing filled with lubricant, then a corresponding loss of lubricant occurs because of passage through the anti-friction bearing.
It is an object of the invention to provide an anti-friction bearing wherein a loss of lubricant because of passage through the anti-friction bearing is avoided during operation and even at high temperatures.
The anti-friction bearing of the invention includes an anti-friction bearing for rotatably journalling a shaft of a gear case of a portable handheld work apparatus. The anti-friction bearing includes: an inner race; an outer race surrounding the inner race at a radial spacing therefrom; a plurality of roller elements disposed between the inner and outer races; a cover disc connected to the inner race; the outer race having an axial inner edge facing toward the roller elements and the inner edge having an axial elevation; the cover disc being arranged in a manner of a seal and extending radially up to the inner edge; the cover disc and the inner edge conjointly defining a radial gap; and, the cover disc having a radial outer edge and the radial outer edge having an axial elevation equal to or less than the axial elevation of the inner edge.
The anti-friction bearing is radially covered by a cover disc which is connected to the inner race of the bearing. In this way, lubricant is especially prevented from axially passing the roller bearing. According to the invention, the cover disc is configured in the manner of a seal which extends from the inner race radially out to an axial inner edge of the outer race which edge faces the roller elements. A minimal radial gap is provided between the cover disc and the axial inner edge of the outer race in order to avoid rubbing between the cover disc and the outer race. If, during the rotational operation of the anti-friction bearing, lubricant reaches the cover disc in the axial direction of the shaft, then the lubricant is tangentially and radially thrown from the cover disc under the action of centrifugal forces without significant volumetric portions of the lubricant reaching the anti-friction bearing through the radial gap and without passing the anti-friction bearing.
In order to make possible a problem-free centrifugal throw-off of the lubricant from the cover disc, it is practical to place the cover disc in the outline of the anti-friction bearing at least in the region of the radial gap, that is, at least the axial elevation of the radial outer edge of the cover disc is equal to or less than the axial elevation of the axial inner edge of the outer race. It can also be practical to so position the end face of the cover disc in the anti-friction bearing that the axial elevation of the end face is equal to or less than the axial elevation of the inner edge. This end face faces away from the anti-friction bearing.
It is practical to form the cover disc as a pressure-insensitive metal part which is resistant to bending. The cover disc is connected at least to a radial outer surface of the inner race to achieve a seal-tight connection of the inner race to the cover disc. It can also be practical to fix the cover disc between a collar on the shaft and an end face of the inner race. Preferably, the cover disc is pressed against the inner race.
To increase the resistance to bending of the cover disc, it is practical to configure the cover disc as being offset in the radial course of its cross section. All types of anti-friction bearings (especially single-row or multiple-row groove ball bearings) are suitable for mounting the cover discs on anti-friction bearings. Anti-friction bearings having corresponding cover discs can also be sealed against the loss of lubricant depending upon the application of the anti-friction bearing.
The anti-friction bearings according to the invention are suitable especially for use for supporting shafts which project through lubricant-filled housings such as gear cases of portable handheld work apparatus such as brushcutters or string trimmers. Here, it is practical to so arrange the particular cover discs of the anti-friction bearings that the cover discs lie in the interior of the particular gear case.